Ring expansion, one-carbon

This procedure illustrates a new three-step reaction sequence for the one-carbon ring expansion of cyclic ketones to the homologous tt,/3-unsaturated ketones. The key step in the sequence is the iron(III) chloride-induced cleavage of the central bond of trimethyl-silyloxycyclopropanes which me obtained by cyclopropanation of trimethylsilyl enol ethers. The procedure for the preparation of 1-trimethylsilyloxycyclohexene from cyclohexanone described in Part A is that of House, Czuba, Gall, and Olmstead. ... 

The reaction of crotonaldehyde and methyl vinyl ketone with thiophenol in the presence of anhydrous hydrogen chloride effects conjugate addition of thiophenol as well as acetal formation. The resulting j3-phenylthio thioacetals are converted to 1-phenylthio-and 2-phenylthio-1,3-butadiene, respectively, upon reaction with 2 equivalents of copper(I) trifluoromethanesulfonate (Table I). The copper(I)-induced heterolysis of carbon-sulfur bonds has also been used to effect pinacol-type rearrangements of bis(phenyl-thio)methyl carbinols. Thus the addition of bis(phenyl-thio)methyllithium to ketones and aldehydes followed by copper(I)-induced rearrangement results in a one-carbon ring expansion or chain-insertion transformation which gives a-phenylthio ketones. Monothioketals of 1,4-diketones are cyclized to 2,5-disubstituted furans by the action of copper(I) trifluoromethanesulfonate. ... 

ONE-CARBON RING EXPANSION OF CYCLOALKANONES TO CONJUGATED CYCLOALKENONES 2-CYCLOHEPTEN-l-ONE... 

Cyclic a-halomethyl or a-phenylselenenylmethyl (3-ketoesters undergo one-carbon ring expansion via transient cyclopropylalkoxy radicals.360... 

The one-carbon ring expansion of (17) to (18) has been accurately measured and proposed as an alternative radical clock to the 5-hexenyl radical to help determine rates in the middle regions of the kinetic scale (Scheme 8). Ab initio calculations have indicated that the isomerization of the 3-oxocyclopentylmethyl radical to the 3-oxocyclohexyl radical is energetically more favourable than the process leading to the ring-opened 5-hexenoyl radical. " ... 

A one-carbon homologation of carbonyl compounds is an important and extensively used method for the preparation of desired carbonyl compounds . One-carbon ring-expansion or one-carbon homologation of ketones or aldehydes via a S-oxido car-benoid is a representative example of the homologation, but few methods have been reported . 

The overall sequence of cyclopropanation of a cyclic silyl enol ether, chlorination with FeCl3, and dehydrochlorination represents a very reliable one-carbon ring expansion method for cycloalkanomer (Table 11). 

Thiopyranylindole 236 underwent ylide-derived Stevens rearrangements when exposed to malonate and cr-ketoester carbenoids and resulted in a one-carbon ring expansion reaction to lead to thiepines <2005JOC746>. Thus, reaction of thiopyranylindole 236 with dimethyl diazomalonate and /-butyl diazoacetylacetate in the presence... 

TMS)3SiH has also been applied for kinetic studies of one-carbon ring expansion in the cyclopentanone series for both primary and secondary alkyl radicals100. 

In the case of trapping of cyclopropenium ions by azirines, the regiochemistry is interpeted in terms of an initial one-carbon ring-expansion 277 ... 

Dowd and coworkers have ingeniously ring-expanded twelve-, fourteen- and fifteen-membered cyclic / -ketoesters using the following sequence. Reaction of the anion of the / -ketoester with diiodomethane followed by treatment with tributyltin hydride with AIBN, in benzene under reflux, gives a one-carbon ring expansion (equation 137)810. 

For a review on one carbon ring expansions of bridged bicyclic ketones, see ref. [2]. 

The high reactivity of compounds containing an episulfonium moiety has been used in an one-carbon ring expansion step [42]. This method is explained at the system shown in Scheme II/8. 1-Vinylcyclopentanol is easily prepared from cyclopentanone (11/50) and vinyl magnesium bromide. The silylation of the alcohols was carried out with re/7-butyldimethylsilyloxytriflate (TBDMSOTf). Using trimethylsilylethers instead of TBDMSO-derivatives side reactions are... 

Scheme II/10. A seleno-mediated one-carbon ring expansion [47] [48].

The most general methods for preparing seven- or eight-membered rings from enamines are by ring expansion of the cyclobutene, cyclobutanone or chlorocyclopro-pane adducts formed by cycloaddition of acetylene carboxylates, ketenes or chlor-ocarbenes, respectively, to enamines of cyclopentanone or cyclohexanone. These are two-carbon or one-carbon ring expansions. Three-carbon ring expansions can also be carried out by cycloaddition of activated cyclopropenes or cyclopropenones. 

The rate of the ring-opening reaction of 5, " and other substrates have been determined using an indirect method for the calibration of fast radical reactions, applicable for radicals with lifetimes as short as 1 ps/ This radical clock method is based on the use of Barton s use of pyridine-2-thione-Al-oxycarbonyl esters as radical precursors and radical trapping by the highly reactive thiophenol and benzeneselenol/ A number of radical clock substrates are known/ Other radical clock processes include racemization of radicals with chiral conformations, one-carbon ring expansion in cyclopentanones, norcarane and sprro[2,5]octane, a-and p-thujone radical rearrangements, and cyclopropylcarbinyl radicals or... 

A fruitful method for formation of 3-substituted cyclohexanones 26 utilizes a one-carbon ring-expansion process starting from 2-substituted cyclopentanones 23. A bromomethyl, iodo-methyl, or phenylselanylmethyl group is introduced at C2 in the jS-position by base-catalyzed alkylation. Treatment of the resulting 2,2-difunctionalized cyclopentanone 24 with tributyltin hydride generates a bicyclo[3.1.0]hexan-l-oxyl radical 25 as a transient intermediate which rearranges and abstracts hydrogen to construct the 3-substituted cyclohexanone 26. 

A useful method of converting 2-substituted cyclohexanones, e.g. 34, into 3-substituted cy-cloheptanones relies on a one-carbon ring expansion via a transient bicyclo[4.1.0]heptan-l-oxy radical. 

One-carbon ring expansion of 2-substituted cycloalkanones 37 (usually / -oxo esters) via transient bicyclo[n. 1.0]alkan-l -oxyl radicals 39 has been extensively exploited as a method of making medium and large ring cycloalkanones 40. " One-carbon ring expansion was also performed with bicyclo[5.3.0]decan-2-ones 41 giving 42 as the product. 

Recently, the sulfonium-ylide pathway has been used repeatedly to perform one-carbon ring expansion by formal insertion of a carbene moiety into a C—S or N—S bond of a cyclic sulfur compound. Examples are compiled in Scheme 37. It can be seen that ring enlargement was successful with thiochroman-4-ones 345 and 348,... 

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